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Fuel Pressure Regulator – FAQ

Fuel Pressure Regulator - FAQ - Do You Have The Correct Fuel Pressure
Fuel Pressure Regulator – FAQ – Do You Have The Correct Fuel Pressure

A fuel pressure regulator, is an integral part of a vehicle’s fuel system.

Most engines use, a fuel pressure regulator now, and there are things that can go wrong with them.

So, your fuel pressure regulator, is designed to keep fuel, within a specific range of pressure.

Consequently, if the fuel pressure regulator, is keeping it out of this range; then the vehicle will not run or will run inefficiently.

So, testing the fuel pressure regulator, is a simple task; that requires some minor equipment and a short amount of time.

Fuel Pressure Gauge
Fuel Pressure Gauge

Firstly, spend the money and get a good, fuel pressure testing gauge. I have heard of people using a Tire Gauge, BUT Don’t, DANGER. Because, the average fuel pressure, can be anywhere from 45 psi to 55 psi. To be sure, consult with your vehicle owner’s manual; for the proper fuel-pressure range, before performing this test.

There are two different problems, that a bad regulator can cause:

Low Pressure

Most problems with fuel pressure, are due to the pressure being too low. The inability of the fuel pump to increase the fuel pressure; up to the vehicle’s specifications, may have several causes:

  • If the pressure is too low; there may not be enough fuel reaching the engine for it to start. Or, if it does start, it may not run efficiently.
  • A fuel leak is a cause of low fuel pressure; although this problem can often be identified; without the need for installing a fuel pressure gauge.
  • Other problems that can cause low fuel pressure include; a kinked fuel inlet line or a clogged fuel filter or strainer.
  • A bad fuel pump in the fuel tank; can also prevent the fuel pressure from reaching the required level.

High Pressure

Fuel pressure that is too high, can cause the engine to run too rich. Common causes of high fuel pressure include; a bad fuel pressure regulator or a clogged return line. Consequently, you will need to perform two different tests; to identify the reason for excessive fuel pressure:

  • The first test requires you to relieve the system fuel pressure; and connect a relief hose to the fuel return line. Place the free end of the hose in a container and activate the fuel pump. The fuel return line is blocked, if the fuel pressure now meets specifications. Otherwise, the regulator may be faulty.
  • The second test requires you to allow the engine to idle; while disconnecting the vacuum hose on the fuel pressure regulator; for vehicles that are so equipped. The regulator may be faulty, if the fuel pressure does not increase by about 5-10 psi.

Too high of pressure may result in, over fueling of the engine. As a result, this can lead to a rough running engine; poor fuel mileage, and black smoke coming from the exhaust. If your regulator is going bad, your car could display several different symptoms.

So, Get Your Fuel Pressure Regulator Checked, If You Notice Any Of The Following:

Spark Plugs Are Black

Remove a spark plug and examine the end of it. If it is sooty, it could be a sign of, a bad fuel pressure regulator. If you find a plug in this condition, check the rest of them. A sooty spark plug could just mean, the engine is burning oil in that cylinder.

Spark Plugs Are Black, Fuel Pressure Regulator
Spark Plugs Are Black

If you end up replacing your fuel pressure regulator, you might also want to replace your plugs. You can try simply cleaning them and putting them back. But, if your engine still runs poorly, get new ones.

Engine Runs Rough

Speaking of poor engine performance; if you are idling the engine and it is not running smoothly; change your oil filter and check your pressure regulator to repair bad fuel pressure.

Engine Runs Rough, Fuel Pressure Regulator
Engine Runs Rough

Another sign that your engine is suffering the effects of a bad regulator is; if you have trouble starting the car. It will turn over a few times, before it actually starts.

The Tail Pipe Emits Black Smoke

Having black smoke coming out of your tailpipe; is a sure sign there is something wrong with your fuel pressure regulator. Replace it.

The Tail Pipe Emits Black Smoke, Fuel Pressure Regulator
The Tail Pipe Emits Black Smoke

The normal color of any smoke coming out of the exhaust; should be white or gray, not black. So, if you see the latter, there is definitely something wrong.

The Dipstick Smells of Gasoline

Check the oil dipstick and see if you smell fuel on it. If you do, it could be a symptom of a bad fuel pressure regulator; which has allowed gasoline to leak into the oil system.

The Dipstick Smells of Gasoline, Fuel Pressure Regulator
The Dipstick Smells of Gasoline

If not repaired quickly it will cause the oil, to lose its lubricating properties. As a result, damaging engine bearings.

Gasoline Drips Out of the Tailpipe

Gasoline dripping out of your tailpipe, is either the result of you overfilling your tank; or a bad fuel pressure regulator.

Gasoline Drips Out of the Tailpipe
Gasoline Drips Out of the Tailpipe

Most likely, the gas is leaking into the exhaust system. Because, the regulator is, allowing it to pass into the lines. As a result, causing major damage to the catalytic converter.

Engine Stalls

If the engine stalls when you press down on the gas pedal, check the fuel pressure regulator. There shouldn’t be any hesitation, when you press on the gas.

Engine Stalls
Engine Stalls

Even if you only notice a little hesitation; get your pressure regulator checked out. Because, it may just be starting to go bad.

Gasoline Is in the Vacuum Hose

If you are noticing any of the signs above; but aren’t convinced that the cause, is a bad fuel pressure regulator; there is something you can do, to be sure one way or the other.

Gasoline Is in the Vacuum Hose
Gasoline Is in the Vacuum Hose

Remove the vacuum hose that attaches to the fuel pressure regulator; making sure the engine isn’t running. So, if gas is in the line, your fuel pressure regulator is bad. Also, if there is none in the line, but when you turn the switch on; fuel drips out of the hose, it is bad.


Finally, we hope that this information we just provided for you; helps you to understand how, fuel pressure regulators work.

Thank You !

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